Power distribution units generally provide current to downstream devices operating at a given voltage. A bus is included in the power distribution unit and acts as a voltage node that provides the current to the devices. The current that is provided to each individual device generally falls within an acceptable range. However, one or more downstream devices may draw more current than normal due to a heavier than normal load or due to a device malfunction. For purposes of protecting both the power distribution unit and the downstream device, it is desirable to block current from the power distribution unit to the downstream device when the current drawn by the device exceeds a threshold amount.
Limiting the current to the downstream device is often done by including a fuse in each line leading to each device from the bus. The fuse often provides an alarm voltage so that when the fuse blows due to excessive current, the alarm is triggered. However, the conventional use of fuses in power distribution busses has drawbacks when multiple lines of power are being provided by the power distribution unit because the alarm circuit of conventional power distribution units indicates that a fuse is blown but does not indicate which line is blocked due to a blown fuse. Furthermore, conventional power distribution units that are configured to operate with fuses are not configured to operate with circuit breakers on some or all lines.
Circuit breakers are used by some conventional power distribution units to limit the current in each line. However, conventional power distribution units using circuit breakers suffer from the same drawbacks as those using fuses. A general alarm is generated by the alarm circuit of a conventional power distribution in response to a tripped breaker, but no indication of the particular line that is blocked is provided. Furthermore, conventional power distribution units that are configured to operate with a circuit breaker are not configured to also operate with a fuse on some or all lines.
It may be useful in some instances to have fuses on some of the lines output by the power distribution bus while having circuit breakers on other lines. Circuit breakers often have an alarming capability that functions by receiving voltage from a voltage source, such as from the alarm circuit itself. Fuses often have an alarming capability that functions by channeling voltage from the power distribution line to the alarm circuitry. Therefore, conventional power distribution units have not permitted interchanging fuses with circuit breakers.
Thus, there is a need in the art for more flexible protection and alarming capabilities for power distribution buses.